1. Field of the Invention
The present invention relates to progressive pressing apparatuses, and particularly, to a progressive pressing apparatus provided with multiple die pressing units for performing pressing on a belt-like plate material or sheet material at multiple stages.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 8-214510 (see paragraphs [0017] to [0019] of the specification, and FIG. 1) discloses a typical progressive die pressing apparatus for manufacturing rotors and stators used in motors. According to such an apparatus, segments of a belt-like steel plate are pressed and punched out to fabricate parts of a rotor, and other segments of the plate are subsequently pressed and punched out so as to fabricate parts of a stator. For performing the pressing operation on a steel plate using such a conventional apparatus, the center of each die that performs the pressing must be set at a predetermined position corresponding to one of the pressing stages provided in the apparatus. Generally, in such a conventional apparatus, each stage is provided with a pressing unit fixed to a predetermined position.
Furthermore, Japanese Unexamined Patent Application Publication No. 5-329699 (see paragraphs [0005] and [0006] of the specification, and FIG. 1) discloses a type of a progressive fabrication apparatus. In this conventional apparatus, multiple pressing units are provided. A cassette is detachably provided on each pressing unit and includes a plurality of pressing means. The apparatus is further provided with a base having dovetail grooves. Each pressing unit is adjustably disposed in the dovetail grooves such that the pressing unit is movable along the dovetail grooves. Each cassette includes a set of a punch and a die. Moreover, a hydraulic cylinder is disposed above each cassette and is provided with an activating rod connected to the corresponding punch.
In the progressive die pressing apparatus disclosed in Japanese Unexamined Patent Application Publication No. 8-214510, the position of each pressing unit of the corresponding stage cannot be readjusted. For this reason, the only way to cope with manufacturing rotors and stators having different diameters is to replace the die assembly with another type. Consequently, for manufacturing rotors and stators that have small diameters, this may be problematic in that the amount of unused areas (unpunched areas) of the steel plate becomes large. To reduce the amount of the unused areas, it is necessary to provide a progressive die pressing apparatus having pressing units that are positioned at a pitch corresponding to the diameter of the stators to be manufactured.
On the other hand, in the progressive fabrication apparatus disclosed in Japanese Unexamined Patent Application Publication No. 5-329699, since the multiple pressing units are adjustably disposed in the dovetail grooves such that each pressing unit is movable along the dovetail grooves, each pressing unit can be shifted to a position suitable with respect to the diameter sizes of the rotor and the stator to be manufactured. Thus, the problem of the large amount of unused areas of the steel plate can be solved. However, the shifting of each pressing unit requires a large amount of force since each pressing unit moves along the dovetail grooves in the base. As an alternative to this structure, the base may be provided with rails in place of the dovetail grooves, and each pressing unit may be provided with, for example, wheels at the bottom portions of the pressing unit so that the pressing unit can be rolled along the rails. However, such an alternative structure may be problematic in that the pressing units may become unstable during the shifting process since the pressing units carry heavy components, such as the hydraulic cylinders and working-oil supplying devices, that are necessary for the pressing operation.